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c#design-patternsgenericscollectionsienumerable
Maxim Gershkovich
Maxim Gershkovich

Reputation: 47169

Why does ICollection<T> implement both IEnumerable<T> and IEnumerable

Why does ICollection<T> implement both IEnumerable<T> and IEnumerable?

What is the purpose of this? How does IEnumerable benefit ICollection<T>?

Upvotes: 6

Views: 1193

Answers (3)

Jon Skeet
Jon Skeet

Reputation: 1500455

IEnumerable<T> itself forces any implementation to also implement the non-generic IEnumerable. This is safe, for the same reasons that IEnumerable<out T> is covariant as of .NET 4... you can always convert the T to object for the non-generic form.

Basically this means that if you've got code which uses a parameter of type IEnumerable, you can still call it with something like List<T>.

Eric Lippert wrote a blog post recently about why collections end up implementing many interfaces, and Brad Abrams wrote a blog post back in 2005 about the specific IEnumerable<T>/IEnumerable decision.

Upvotes: 13

Andrew Cooper
Andrew Cooper

Reputation: 32576

IEnumerable<T> inherits IEnumerable so it makes sense for ICollection<T> to as well. It's just stating explicitly the inheritance that would be there anyway.

Upvotes: -1

escargot agile
escargot agile

Reputation: 22379

The non-generic interface is for backward compatibility. If you write code using generics and want to pass your collection to some module written in .NET 1.0 (which doesn't have generics) you still want this to succeed, and you want the old method to be able to iterate through it.

Upvotes: 10

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